1. Field of the Invention
The present invention relates to an image forming apparatus related to a printer such as a laser printer that scans an image with a laser beam to form an electrostatic latent image on a photoconductor drum. Particularly, the present invention relates to an image forming apparatus comprising a printing side and a host side that can easily check urgent statuses of the printing side, and to an image forming apparatus that enables a host side to easily adjust a video data signal transmission timing in response to a change in a recording density of a printing side.
2. Description of the Related Art
There is described an image forming apparatus related to the present invention which has a printing side comprises a printer, and a host side comprises a controller. The printer transmits a status signal to the controller, and, according to the status signal, the controller transmits a command to the printer to carry out a printing process. Namely, the controller checks a state of the printer according to the status signal and sends the command that controls an operation of the printer.
For example, such related image forming appartus is disclosed in Japanese Patent Publication No. 32543/1983 and Japanese Patent Publication No. 45982/1984.
To improve the operability of such an image forming apparatus, the applicant of the present invention has already disclosed a system provided with exclusive interface signal lines for transmitting signals such as a print request signal and a page end signal from the printing side to the host side.
However, due to the exclusive interface signal lines added between the printing side and the host side, a circuit constitution of the system is complicated to raise a need of simplifying the system.
To improve the operability without adding the interface signal lines, there has been proposed another system that uses a system program provided for the host side to always check urgent statuses such as a print request status, a print data request status and an image transferring status of the printing side.
However, load of the host side will be increased if the urgent statuses shall always be checked by the system program of the host side, because the exclusive program for always checking the urgent statuses shall be added to a main program of the host side, and because an overall processing time of the host side shall be extended due to the execution of the exclusive program.
According to the related apparatus, the printer 2 outputs a horizontal synchronous signal to the controller and, in response to this signal, the controller transmits a video data signal to the printer. Therefore, if a recording density of the printing side is changed, the host side shall change a transmission timing of the video data signal and a transmission time for one dot of the video data signal according to the recording density of the print side.
Namely, a time interval "t" between a point "a" at which the horizontal synchronous signal is generated and a point "b" at which the video data signal is transmitted shall be changed according to a change in the recording density of the printing side. A time interval t1 is for a small recording density, while a time interval t2 is for a large recording density, and t2 is greater than t1 (t2&gt;t1).
As described in the above, the host side of the conventional image forming apparatus transmits the video data signal to the printing side according to only the horizontal synchronous signal outputted from the printing side. Therefore, if a recording density of the printer is changed, the host side shall execute a process for changing the transmission timing of a video data signal and a process for changing the transmission time for one dot of the video data signal according to the changed recording density. As a result, a processing time of the host side will be elongated.